Frank Lloyd Wright is widely considered the greatest modern American architect. And for good reason — Wright imbued his structures with natural light and pioneered innovative, open floor plans that forever changed the way people thought about housing and architecture. Plus, he was a prolific designer — he worked on more than 400 buildings, and no two are exactly alike.

But nobody's perfect. Innovation almost always comes at a cost.

Here are seven things Wright got wrong about design.

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His roofs weren’t properly supported.

Fallingwater in Mill Run, Pennsylvania
via/flickr

Wright's most famous architectural oversight is the lack of structural support for Fallingwater, his most iconic work. Built over a waterfall, the 1939 house blends beautifully into the surrounding landscape, its cantilevered floors jutting out like the rocks in the stream below.

But in 2001, Fallingwater made news because it was literally at risk of falling into the water. Though the engineer working with Wright when it the house was built suggested there was not enough steel support to hold up the concrete, Wright overruled him. But Wright was wrong, and the home's beams eventually began to crack and give way. A massive renovation was needed to keep the structure intact and safe for visitors.

According to Eifler, this oversight is common among Wright's buildings. "He was very interested in getting things built, and sometimes he would under-structure roofs," he explains. "So we have put a great deal of steel in his roofs to make them not droop."

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Many buildings leaked.

Hollyhock House in Los Angeles, California
Joshua White

Jeffrey Herr, the curator of Hollyhock House in LA, says the striking building had several flaws from the get-go.

"The roof design itself had some interesting design issues that almost guaranteed water penetration," he explains.

Hollyhock House has undergone many renovations throughout its 90 years, the most recent of which cost $4.5 million. Herr estimates the total cost of upkeep since it was built likely totals around $20 million. But he's emphatic that the cost has been worth it.

"There is no other architect that has ever done anything like Hollyhock House. There isn't any other structure like it either in his oeuvre or in anybody else's," Herr says.

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Concrete foundations were often too weak.

John Eifler says that when beginning a Wright restoration project, he always looks for settlement. That's because Wright often tried to figure out ways to avoid the cost of pouring concrete into the ground to build a strong foundation.

"That drove him nuts, I think," Eifler explains. "He was always trying to find another way to hold up the building without having to spend so much money on basements and concrete."

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Wright didn’t fully consider future maintenance or upkeep.

Chicago architect Gunny Harboe, who has worked on six Wright renovation projects — including the well-known Taliesin West — says Wright and German-American architect Mies van der Rohe shared a lack of concern for the durability of their structures.

"They didn't really understand how things would perform over long periods of time, nor did they probably care about it," Harboe says. "They were more interested with making something that was in their mind, what they wanted to make, and doing it in a beautiful way. And how that would get dealt with in the future was sort of left up to others."

That's created problems for owners of Wright buildings, of course, but Harboe is also quick to note that the architects were working nearly a century ago, when that outlook was not considered as much of a flaw as it is now, with today's emphasis on durability and sustainability.

John Eifler also suggests that Wright likely believed the imminent arrival of new technologies would solve many current design problems.

"The modernist architects especially after WWII were very strong believers in technology that may not have existed then, but they were convinced it was just around the corner," he says.

So perhaps Wright simply just hoped that new materials would become available that could better maintain his houses.

Wright’s drainage systems weren’t always up to the task.

Gunny Harboe has led the renovation of Unity Temple, one of Wright's only designs for a religious space. The building is considered a masterpiece, and has been nominated to become a UNESCO World Heritage Site, along with Hollyhock House and eight other Wright buildings.

"One of the big problems at Unity Temple has been the fact that the internal drainage system was undersized," Harboe says. "It was never really big enough to accommodate the amount of water that wanted to go through it."

Jeffrey Herr says the drainage system in Hollyhock House also had to be replaced.

Wright prioritized aesthetics above all else.

Wright did not always adhere to the principle that form follows function. Creating buildings that are now considered works of art meant that practical boundaries had to be pushed.

And, though architects of today would most likely be criticized for that, those who know Wright's work almost universally agree that he shouldn't be blamed for adhering so stubbornly to his visions.

"He was thinking of new materials and new ways of putting things together — that's what has really impressed me now that I've worked on so many," John Eifler says. "I can never assume I know how something's made."